Soft Body Animation to Keyframe Animation
I managed to do it, you need the add-on "Animation: Corrective Shape Keys" though. You can just enable it in your blender preferences.



What you do is you bake your animation, and then at the frame where you want to keep the shape of the softbody and animate it by hand you go into the shapekeys menu and click "create duplicate for editing". 


This will create a duplicate of your object that looks exactly like if the SB modifier had been applied, however maybe with different transforms, but that doesnt matter. Select the new duplicate, then select the original (so it's the active object), and again go into the shapekeys menu. This time press "join as shapes". Your object now has a shapekey of that "applied" shape. Set it to 1, and then at the point where your softbody assumes that shape, keyframe the render-/viewport-display of the modifier to disabled. Because this shape is also active as a shapekey you will not notice that the softbody has been deactivated, but you can now transform it like a normal object again, if however with a weird origin point.

If I misunderstood your question and you want to know how to have your keyframes influence the actual SB simulation, you can do this:


Again, get to the point where you want to use your keyframes on the object. Do the "create duplicate for editing" thing again, give it the same transforms as the original. Set its origin to geometry. Link the softbody modifier (ctrl+L) from the original so you don't have to retype all the values, and enable goal. Keyframe the min and max goal values to be 1 at the first frame so it really takes on that default shape, and then min back to 0 at the next frame. Because you have goal active it should now take the transform keyframes into account, and just need to hide the original at that frame. Basically one object does the first half of the animation, the second one the other. You can use goal from the beginning but then you'd have to animate gravity by yourself and pay attention to other stuff. There might be other ways but honestly dealing with SB is often a pain the butt.

You could also try forces, but I never used them myself so I can give no information about that.